North Korea launched another missile early Saturday morning, making it the regime's third successive, yet unsuccessful missile test since April.
That means, McMaster said, working to enforce current United Nations sanctions and perhaps ratcheting them up.
South Korea's Foreign Ministry went even further saying Pyongyang was "playing with fire" and warned of tougher sanctions.
"And it also means being prepared for military operations if necessary", he said.
North Korea's latest missile test came hours after U.S. Secretary of State Rex Tillerson encouraged United Nations members Friday to pressure against Kim Jong Un's regime.
Meanwhile, North Korea's state media on Saturday reiterated the country's goal of developing a nuclear missile capable of reaching the continental US.
McMaster said that Trump 'has made clear that he is going to resolve this issue one way or the other, ' but that the president's preference is to work with China and others to resolve it without military action, such as through sanctions. "We'll see what happens".
In the CBS interview, the U.S. president was asked about why the North's rockets keep blowing up.
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Now factor in the Celtics who are 20th in the league in total payroll yet they've managed to secure the top seed in the east. James will see the same assortment of bodies thrown at him and expect Tucker to be the guy there in late game situations.
Mr Trump told Reuters in an interview on Thursday a "major, major conflict" with North Korea was possible and praised Chinese leader Xi Jinping for "trying very hard" to rein in Pyongyang.
Host John Dickerson presses Trump on what specifically he means by "not happy" but, rather than elaborate, Trump just repeats "I will not be happy" in a slightly more menacing tone.
Pressed on whether that would lead to a military strike, Trump said: "I don't know. We'll see what happens", the president said. Is the pressure not working?
North Korea test-fired a mid-range ballistic missile Saturday in apparent defiance of warnings from the United States as a U.S. supercarrier conducts drills in nearby waters.
But McMaster and South Korea's presidential security adviser Chairman Kim Kwan-jin spoke on Sunday to confirm that the US won't seek money from Seoul to pay for the Thaad system.
A spokesperson for South Korea's presidential office said on Sunday that McMaster told South Korean National Security Adviser Kim Kwan-jin in a phone call that a pre-existing funding arrangement would remain in place. "I just don't want people to know what my thinking is", Trump maintained.
"In a nutshell, DPRK have already declared not to attend any type of talks which would discuss its nuclear abandonment, nuclear disbandment", Kim In Ryong said. "So obviously, he's a pretty smart cookie", Mr Trump said.
The test is the state's fourth straight unsuccessful missile test since March.
Barely 24 hours ago, North Korea tested a short range missile that failed instantly, in the face of widespread worldwide pressure.